It is common to enhance the properties of a composite part by applying a polymer coating to the surfaces of the part. Reinforced composite materials are used to fabricate many components due to their light weight and high strength. However, in certain applications, such as where high temperatures, chemical exposure or high erosion are expected, such composites are not used, as composite properties will typically degrade in such environments. To overcome this, a barrier coating may be added to a composite part. For example, a glass fiber reinforced epoxy part may have a thermal barrier coating added to it to protect the part at high temperatures. Similarly, other coatings, such as thermoplastic coatings may be applied to enhance properties such as corrosion resistance.
The method used to apply these coatings typically requires first production of the part and post production addition of the desired coating layer by either adhesive bonding or thermal spraying a property protecting material onto the part.
In U.S. Pat. No. 5,021,259, a method of applying a continuous thermoplastic coating in one coating step is discussed. A thermoplastic polymer is applied to a porous metal surface at a temperature which provides a semi-fused highly coarse coating. The coating and surface are then heated such that the coating flows and locks into the pores in the substrate.
In coating molded composites, there is a lack of porosity on the external surfaces and the usual methods of application suffer from the inability to lock the coating to the part. Consequently, other post production steps such as sandblasting to roughen up the surface may be required before coating can be undertaken. If the bond between the coating and part surface is not uniform, there is the potential for separation and localized coating failure.